In general, a battery (secondary battery) is reduced in its internal activation level at low temperature than at normal temperature and its internal resistance is increased. For this reason, even though the current is identical when the battery is discharged, the voltage between both ends is significantly reduced by the internal resistance. Battery performance is limited by the voltage between both ends. Therefore, the continuously dischargeable duration is shortened with reduction in the battery temperature and the amount of power that can be supplied from the battery is reduced. As for charging, the voltage between both ends is more steeply raised with reduction in the battery temperature and the continuously chargeable duration is shortened.
To cope with this, in recent years, to forcibly raise the temperature of a battery when the battery is at low temperature to promptly ensure its charge/discharge performance, charging/discharging of the battery is forcibly carried out to accelerate the production of Joule heat within the battery and the temperature of the battery is thereby internally raised.
In JP 2001-314039A (US 2002/003417), for example, battery temperature is detected by a temperature sensor and a remaining capacity control center value (SOC target value) of the battery is set according to this battery temperature. When the battery temperature is low, the remaining capacity control center value is shifted to the upper side of a remaining capacity control range. Then charging/discharging of the battery is controlled based on the deviation between this remaining capacity control center value and the actual remaining capacity (SOC). The production of Joule heat within the battery is thereby accelerated to raise the temperature of the battery.
As the charging/discharging current of a battery is increased, its Joule heating is increased and its temperature can be more quickly raised. In the above technique, however, charging/discharging power is controlled according to the temperature and remaining capacity of a battery. Therefore, when the internal state of the battery (for example, the internal resistance, the state of internal polarization, and the like) changes, it is likely that the charging/discharging power of the battery may go out of an appropriate range. In the temperature rise control, as a result, the charging/discharging power of the battery is excessively limited and this results in delayed temperature rise in the battery. Conversely, it is also likely that excessive charging/discharging power is passed and the battery abnormally produces heat and this leads to deterioration or breakage of the battery.
In JP 2007-28702A and JP 2007-12568A, the production of Joule heat within a battery is accelerated to raise the temperature of the battery by repeating charging and discharging of the battery alternately and periodically when the battery temperature detected by a temperature sensor is low.
When either charging or discharging of a battery is only continuously carried out for a long time, the polarizing effect of the battery is increased and significant voltage change occurs. As a countermeasure therefor, it is effective to alternately and periodically repeat charging and discharging during the execution of the temperature rise control. However, the cycle of switching between charging and discharging and the current amplitude (power amplitude) for achieving optimum temperature rise vary depending on the internal state of the battery that varies from hour to hour. Such internal state of a battery includes not only remaining capacity and battery temperature but also internal resistance, production tolerance, deterioration, and the like. Therefore, it is preferable to vary the cycle period and the amplitude according to the internal state of a high-voltage battery with respect to the cycle period and amplitude of charging/discharging for bringing out the maximum temperature rise performance. However, the cycle period or amplitude of charging/discharging for achieving optimum temperature rise may be difficult to implement depending on the type of electrical equipment used for the temperature rise control. For example, when the cycle period of charging/discharging is too short to meet the performance limit of the electrical equipment or the amplitude is too large to meet the performance limit of the electrical equipment, the following takes place: the current of the electrical equipment exceeds an allowable current; therefore, there is a possibility that the optimum cycle period or amplitude cannot be achieved. As a result, the performance of the temperature rise control is degraded and temperature rise in the battery is decelerated.
Further, when a boost converter is used to repeat periodical charging/discharging, the following takes place: input/output current to a capacitor of the boost converter is produced and vibration noise is produced in the capacitor. In JP 2008-78167A (US 2008/0068775), a cushioning material layer for absorbing vibration is added to the interior of a capacitor to reduce this vibration noise. In JP 2008-66503A, the electrode plane of a capacitor is formed of resin material low in coefficient of elasticity by molding.
In JP 2008-162397A, in a hybrid vehicle in which the driving force of a motor is transmitted through a gear box, when gear rattle in a gear is caused by fluctuation in the driving force of the motor, engine output correction or the like is carried out.
According to these conventional technologies, however, the following occurrence is expected depending on the cycle period or amplitude of battery charging/discharging in the temperature rise control: the effect of reducing noise such as vibration noise may be insufficient or the effect of reducing fluctuation in driving force may be insufficient.